This invention relates to an induction system for an internal combustion engine and to a method of operating an engine and more particularly to an induction system and method of operating an engine to improve performance under certain types of transient conditions. As is well known, the induction system for an internal combustion engine is particularly important in determining the performance of the engine. Induction systems in conventional engines generally represent a compromise between the free-breathing type of induction systems that provide high performance by introducing the charge into the combustion chamber in an unrestricted fashion and without introducing turbulence to the inducted air charge and the low speed or mid-range type of induction system that provides a higher flow velocity and turbulence in the combustion chamber. The free breathing system, although it permits maximum charging and high performance, will provide less than desirable performance under low speed, low load conditions. An induction system that provides good performance under low load conditions, however, will not offer the ability to induct sufficient air so as to achieve maximum performance. Therefore, it has been the practice with conventional engines to compromise the induction system between these two extremes.
There have also been provided induction systems that include devices for introducing turbulence and/or high velocity to the intake charge under some running conditions and substantially unrestricted induction under high speed high load conditions. One such system is described in the co-pending application of Yoshiharo Isaka entitled "Tumble Control Valve for Intake Port," Ser. No. 07/834,604, filed Feb. 12, 1992, and assigned to the assignee hereof. This system shows a number of embodiments of induction systems wherein there is provided a control valve in the intake passage which is moveable between a first, opened position in which unrestricted charging is provided and wherein the charge flows into the combustion chamber in a generally axial direction for high speed running. Under low speed or mid-range performance, the control valve is moved to another position wherein the charge which enters the combustion chamber is redirected so as to increase the turbulence in the combustion chamber and also the velocity at which the charge is inducted. The turbulence is generated by introducing either a tumble and/or a swirl to the intake charge. Tumble is generally referred to as a type of swirl that occurs about an axis that extends transversely to the axis of the cylinder bore. Swirl, on the other hand, is the type of motion in which rotation occurs about an axis that is coincident with or parallel to the cylinder bore axis.
In the systems shown in that application, the position of the control valve is set in response to certain engine running parameters, normally speed and/or load. This system is extremely effective in providing good performance throughout the entire engine speed and load ranges.
However, there is another type of condition wherein modification of the amount or direction of swirl and/or tumble may be desirable. This other type of condition is a transient condition wherein the engine is not operating at a steady state condition but rather is changing its state. Examples of such transient conditions are during idle when attempts are made to stabilize idle speed, when emission control is being practiced by attempting to run on a lean mixture and to reduce nitrous oxide emissions through the use of exhaust gas recirculation (EGR) or on starting and/or cold warmup. Under these conditions, variations in the steady state position of the control valve can significantly improve performance and reduce the emission of unwanted hydrocarbons and other constituents in the exhaust gases.
It is, therefore, a principal object of this invention to provide an improved induction system and induction method for an internal combustion engine which permits good performance under all running conditions including transient conditions.
It is a further object of this invention to provide an improved induction system and method of introducing an intake charge to an engine that will improve performance under transient conditions by providing the desired amount of turbulence in the combustion chamber for the specific transient condition.
It is yet a further object of this invention to provide an improved method and apparatus for controlling the idle speed of an engine to maintain idle speed stability.
It is a still further object of this invention to provide an improved induction system and method for inducting a charge into an engine that will permit the use of increased amounts of exhaust gas recirculation for emission control.
It is a still further object of this invention to provide an improved induction system and induction method for an internal combustion engine that will improve engine performance under starting.
It is still another object of this invention to provide an improved induction system and induction method for an internal combustion engine to improve performance under cold warmup.
As has been previously noted, the use of exhaust gas recirculation is a very effective method for reducing the emission of certain exhaust gas constituents. However, all engines are sensitive, to varying degrees, to the amount of exhaust gas recirculation which they can tolerate and still maintain stable running. With convention induction systems, the EGR tolerance is such that the desired amounts of exhaust gas recirculation cannot be employed under all running conditions.
It is, therefore, a still further object of this invention to provide an improved induction system and method for introducing a charge to the combustion chamber that will permit the use of increased amounts of EGR under at least some running conditions.